The human consumption of fats in various foodstuffs contributes significantly to obesity. High fat diets also contribute to various human diseases such as heart and coronary diseases. One method of reducing obesity and/or diseases such as heart and coronary diseases in the human population is to reduce the consumption of fat. In recent years, fat substitutes or low-calorie fats have attracted increasing attention as a method of reducing the fat and calorie content of foodstuffs. The objective is to provide edible fats with reduced absorption and digestive properties with minimal side effects and with acceptable taste and feel characteristics when incorporated into food compositions.
Transesterification reactions have been used to prepare saccharide polyesters with reduced absorption and digestive properties. Such transesterification reactions generally required high temperatures and/or toxic solvents (such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, and the like) and were not, therefore, generally suitable for the preparation of fat substitutes for use in food applications.
For example, Rizzi et al., U.S. Pat. No. 3,963,699 (issued Jun. 15, 1976), provided a solvent-free process whereby sucrose and fatty acid lower alkyl esters are simply heated together in an inert atmosphere at or above the melting point of sucrose (about 185.degree. C.). After only a few minutes at 185.degree. C. or above, sucrose begins to decompose which leads to undesirable by-products. This reaction mixture of Rizzi et al. is heterogeneous due to the mutual insolubility of sucrose and the fatty acid lower alkyl esters. Attempts to increase the solubility of sucrose in the transesterification media have generally lead to increased caramelization. Alkali soaps and alkali-free soaps have also been used to retard the rate of sucrose decomposition at the elevated temperatures of the process. Attempts have also been made to improve the yields by employing catalysts and varying reactant ratios (see, e.g., U.S. Pat. Nos. 4,517,360 and 4,518,772). This solvent-free transesterification process has, however, significant problems of its own. For example, the soaps used to retard the thermal decomposition of sucrose must be removed from the reaction products. And even with the addition of such soaps, the products are still contaminated with sucrose decomposition products resulting from thermal cracking or caramelization. The sucrose polyester products are, therefore, often colored (see, e.g., U.S. Pat. Nos. 3,963,699, 4,517,360, 4,518,772, and 4,611,055). Problems are also encountered in attempting to prepare a homogeneous melt of the sucrose and fatty acid ester mixture because the reactants at the reaction temperature are viscous and tend to agglomerate when stirred (see, e.g., U.S. Pat. No. 3,792,041). The sucrose fatty acid ester intermediates that are formed also have a tendency to hydrolyze or saponify under the reaction conditions (see. e.g., U.S. Pat. No. 3,792,041); such side reactions lead to further contamination of the desired sucrose polyester products. The poor affinity of the reactants for one another and the excess of fatty acid esters in the reaction mixture, which is generally necessary to obtain the desired high degree of transesterification, results in a reaction mixture which is susceptible to phase separation (see. e.g., U.S. Pat. No. 4,611,055). Such phase separation will, of course, adversely affect the transesterification reaction.
Akok and Swanson, 55 J. Food Sci., 236 (1990), employed sucrose octaacetate rather than sucrose in a transesterification reaction. Sucrose octaacetate has increased solubility in the fatty acid ester reactants and, therefore, provides a more homogeneous reaction system along with better yields of the sucrose fatty acid polyester and lighter colored products (i.e., reduced caramelization and other decomposition reactions). This procedure, however, generates large amounts of by-product methyl ester (i.e., on average, eight moles of methyl acetate are produced for each mole of sucrose octaacetate reacted). Methyl acetate is a highly flammable material which generally must either be disposed of in an environmentally acceptable manner or converted to acetic acid for reuse or recycling.
More recently, Meyer et al., U.S. Pat. No. 4,840,815 (issued Jun. 20, 1989), and Meyer et al., PCT Publication WO 92/0360 (published Mar. 5, 1992), provided a one-stage, solvent-free, low-temperature, low-pressure process for the preparation of saccharide fatty acid polyesters. The Meyer et al. process involves reacting a mixture of a lower acyl ester saccharide, a fatty acid lower alkyl ester, and an alkali metal catalyst at a reaction temperature of 100.degree. to 125.degree. C. while drawing a vacuum of less than about 15 torr over the reaction mixture. The saccharide fatty acid polyesters are reported to be formed via a transesterification reaction whereby at least a portion of the lower acyl ester groups on the starting saccharide are replaced with the fatty acid groups from the fatty acid lower alkyl ester. Mieth et al., German Patent 227,137 A1 (laid open Sep. 11, 1985), provides a method for preparing polyol-ester mixtures suitable for use as fat substitutes whereby saccharides are esterified or transesterified with short-chain carboxylic acid derivatives in the presence of a catalyst and then reacted with triglycerides having long-chain carboxylic acid derivatives (i.e., pig grease or hard rape fat) at a temperature of 120.degree. to 140.degree. C. The polyol-ester mixtures so produced can be subjected to further transesterification reactions at 100.degree. to 120.degree. C. using longchain carboxylic acids or their esters as reagents. The catalysts used by Mieth et al. include phosphorous acid, alkali metals, alkali alkylates, and alkali salts of weak acids.
It is desirable to provide a new method for the production of saccharide fatty acid polyesters, especially sucrose fatty acid polyesters, which overcome at least some of the problems encountered in the prior art. It is also desirable to provide a new method for the production of saccharide fatty acid polyesters, especially sucrose fatty acid polyesters, which results in less caramelization and/or decomposition products and which generates reduced amounts of by-product low molecular weight esters. The methods of the present invention are generally easier to use and provide better saccharide polyesters than the methods of the prior art. The methods of the present invention generally result in less caramelization and generate significantly less by-product low molecular weight esters during the transesterification reactions.